Low-density sealing mass, ground mass and method for producing the same and the use thereof

ABSTRACT

The invention relates to a sealing mass with low density and improved tensile strength on the basis of sulfur-containing polymers such as on the basis of polysulfide, polyether or/and polytioether that has a density of not more than 1.3 g/cm 3  according to ISO 2781 and a tensile strength of at least 1.9 N/mm 2  according to ISO 37 after curing. The invention further relates to a ground mass based on sulfur-containing polymers for producing a sealing mass that comprises at least one long-chain linear polymer and at least one short-chain branched polymer having a content in trifunctional molecules, or/and at least one multifunctional cross-linker with a number of functional groups n≧3. The invention further relates to a method for producing a sealing mass according to which at least one base polymer is mixed with at least one adhesion promoter and the at least one light filler, especially hollow filler, is added, a vacuum with a remaining pressure of less than 50 mbar being maintained during incorporation of the light filler.

The invention relates to a low-density sealing composition withincreased tensile strength based on sulfur-containing polymers and alsoan accompanying base composition and a process for their manufacture.

The sealing composition of the invention is intended to serve inparticular for the bonding or gluing of parts and/or the sealing orfilling of cavities and interstices. This is of particular interest inaviation and space travel, but also anywhere where, as a result of alarger quantity of sealing compositions, particular attention must bepaid to the weight used, in other words to the density of the sealingcompositions, as e.g. with land vehicles.

Sealing compositions are now used for the widest variety ofapplications. They serve in particular for the sealing of constructionelements, the gluing e.g. of sheets to existing structures such as e.g.sections of an aircraft or to protect against corrosion in areas wherethe anti-corrosion layers of metal elements have been damaged or removede.g. in the vicinity of drill holes and may temporarily assume asupporting function e.g. during the transport of structures underconstruction, which are subsequently fitted with permanent supportingjoining elements.

In principle, two process variants are possible for manufacturinglow-density sealing compositions: Either hollow filling bodies are usedwhich, as a result of a gas-filled cavity, are manufactured with a verylow density. Or fillers in compact form can be added which, as a resultof their low density in comparison with the density of the othercomponents of the sealing composition, such as e.g. inorganic fillers,are particularly light and thus help to reduce the density overall.However, to the knowledge of the applicant, the production oflightweight sealing compositions has reached its limit at a minimum of1.30 g/cm³, as the base polymer itself has a density in the range of 1.0to 1.3 g/cm³ and as the fillers used hitherto have a densityapproximately in the range of 2 to 4 g/cm³.

Particular demands are now made of sealing compositions for theproduction and maintenance of air- and spacecraft. As a result of theiruse in the sealing of fuel tanks, protection against corrosion,aerodynamic smoothing and sealing of the pressure hull, great emphasisis placed on elasticity over a wide temperature range, resistance tovarious media such as e.g. fuel, hydraulic fluid, condensation andanti-freeze fluid and a good sealing and bonding action on the widestvariety of substrates.

In addition, in the case of interlayer sealing compositions, it isdesirable that such compositions have no hollow bodies or cavities.

It can be assumed that ca.1000 to 2000 kg sealing compositions are usedin the construction of an airliner. If, therefore, the density of thesesealing compositions could be reduced by e.g. 10 to 30%, this wouldresult in a tangible reduction in weight: e.g. from a density of ca.1.5g/cm³ to ca.1.28 g/cm³ or in some cases even to ca.1.1 g/cm³.

U.S. Pat. No. 5,663,219 discloses a sealing composition based onpolysulfide, the sealing composition having a density in the range 1.0to 1.3 g/cm³ and a peel strength in the range above 17 pounds per linearinch. This specification gives a density below 1.3 g/cm³ only once inthe examples, namely 1.1 g/cm³ in example 1, but gives no furthermechanical typical data for this. On the basis of the remaining data andknowledge of the formulations, it is assumed that the peel strength ofthis sealing composition is rather low. The best average value given forpeel strength, which is given for example 10, is 28.3 pounds per linearinch (a 124 N/25 mm). No tensile strength data are given for this.

The object was therefore to propose a sealing composition with as low adensity as possible, but at the same time with good mechanicalproperties and a manufacturing process for these sealing compositionsthat is as simple as possible, and that can be manufactured withpolymers that are as economic as possible and that also has a widevariety of applications. Above all, these sealing compositions shouldalso be extremely suitable for use in aerospace applications.

The object is achieved by a sealing composition of low density andincreased tensile strength based on sulfur-containing polymers such ase.g. on polysulfide, polyether and/or polythioether, which ischaracterised in that it has a cured density of no more than 1.3 g/cm³determined to ISO 2781 and a tensile strength of at least 1.9 N/mm²determined to ISO 37.

For the sake of linguistic simplicity, the term sealing composition inthe context of this invention is used below in some cases in such a waythat it comprises, in addition to the cured sealing composition, alsothe concept of the base composition and the base composition when mixedwith the hardener (e.g. based on manganese dioxide with accelerators,wetting agents etc). The term base composition describes a mixture whichafter mixing with the hardener and after curing with the hardener isnormally understood to be a sealing composition. A content of hardenerin relation to base polymer in the range of 5:100 to 15:100 is mostlyused.

The sulfur content of the sealing compositions according to theinvention may already be contained in the base polymer—e.g. in thepolysulfide, polythioether or polyether with individual sulfur bridges(as single and/or double bridges), or may be introduced by means of theterminal mercapto groups. The base composition comprises the basepolymer of the sealing composition according to the invention, intowhich the other components are mixed or have been mixed. The proportionof the base polymer in the total sealing composition is conventionally50 to 85 wt. %, preferably 55 to 82 wt. %, particularly preferably 62 to78 wt. %. A higher proportion of fillers and/or hollow filling bodies isto be added to the base polymer, on the one hand to reduce the densityas far as possible and on the other to set the highest possiblemechanical properties. The base polymer mostly has a density in therange of 1.0 to 1.4 g/cm³, in the case of the polysulfide base polymerapproximately of 1.29 g/cm³. The chain length of the base polymer maypreferably be in the range of 1000 to 8000 g/mol, particularlypreferably in the range of 2000 to −5000 g/mol, most preferably in therange of 2500 to 4500 g/mol. The chains of the base polymer may bepurely linear or crosslinked to a limited extent. The proportion ofcrosslinking is preferably 0 to 90%, in particular 20 to 80%, mostparticularly at least 40% or up to 70%, in each case in relation to thenumber of the chains, the molecular weight in relation to the percentageby weight being taken into account.

Surprisingly, it was found that at least one long-chain linear polymer(e.g. at least one linear polysulfide with a chain length in the rangeapproximately of 1500 to 5000 g/mol, in particular in the rangeapproximately of 2000 to 4500 g/mol such as e.g. LP 541 from Rohm & Haasor G 10 from Akzo Nobel) in combination with at least one short-chain,branched polymer (e.g. at least one branched polysulfide with a chainlength in the range approximately of 500 to 2000 g/mol, preferably inthe range approximately of 800 to 1500 g/mol, in each case with acontent of trifunctional molecules in the range of 0.1 to 5 mol %, inparticular with a content in the range of 0.5 to 2 mol %, such as e.g.LP 3, LP 33 from Rohm & Haas or G 44, G 4 from Akzo Nobel) and/or atleast one polyfunctional crosslinker—optionally partially or wholly as asubstitute for the short-chain polymers—with the number of functionalgroups n≧3, produces particularly good mechanical properties. Preferablyn=3 and/or 4, but in principle can also take on values of n=3, 4, 5, 6,7 and/or 8, but rarely values for n greater than 8. The polyfunctionalcrosslinker may be mercapto-functional e.g. as in the case ofpentaerythritol-tetrakis-3-mercaptopropionate, trimethylolpropanemercaptopropionate or trimethylolpropane trimercaptoacetate from BrunoBock, or epoxy-functional as in the case of the triglycidyl propylaminophenol TGPAP from Shell, Araldit® MY 0500 and Araldit® XU MY 0505 fromCiba or DEN 431 from Dow. The content of crosslinkers may vary from 0 to5 wt. %, preferably, where crosslinkers are added, 0.1 to 3 wt. %,particularly preferably no more than 0.5 wt. %. The chemical variants ofthe base polymer and the crosslinker are known in principle to theperson skilled in the art.

In addition, the base composition may contain at least one adhesionpromoter. This serves to bind the fillers and hollow filling bodies intothe polymer and to aid adhesion to the substrate. Where used, it isnormally contained in a total quantity of 0.1 to 8 wt. %.

Furthermore, the base composition may contain at least one mineralfiller. This may be a filler e.g. based on aluminium oxide, aluminiumhydroxide, chalk, silica, silicates and/or sulfates. The total contentof these may vary from 0 to 49 wt. %, preferably 1 to 40 wt. %,particularly preferably at least 2 wt. % or up to 30 wt. %, mostparticularly preferably at least 5 wt. % or up to 25 wt. %.

Furthermore, where needed, it may contain in particular at least oneeach of a rheological additive to establish e.g. the thixotropy and/orthe flow properties, a biocide, a corrosion inhibitor or an additivewith a different action.

In addition, the object was achieved with a base composition based onsulfur-containing polymers for the manufacture of a sealing composition,which is characterised in that it contains at least one long-chainlinear polymer, in particular at least one linear polysulfide with achain length in the range for instance of 1500 to 5000 g/mol, and atleast one short-chain, branched polymer, in particular at least onebranched polysulfide with a chain length in the range approximately of500 to 2000 g/mol, which has a content of trifunctional molecules, inparticular in the range of 0.1 to 5 mol % and/or at least onepolyfunctional crosslinker with the number of functional groups n≧3.Instead of the content of trifunctional molecules, higher-functionalmolecules may in principle also be used at the same time or as analternative in particular up to n=8. The linear polysulfide preferablyhas a larger proportion, largely or even wholly, of a linear chain witha functionality of 2, i.e. two terminal functional groups.

Furthermore, the object was achieved with a base composition based onsulfur-containing polymers for the manufacture of a sealing composition,which has a density before the addition of a hardener not exceeding avalue of 1.285 g/cm³, in particular a value of up to 1.28 g/cm³,preferably a value of up to 1.26 g/cm³, most preferably of up to 1.23g/cm³, above all a value of up to 1.18 g/cm³, in particular a value ofup to 1.12 g/cm³.

The density e.g. of the liquid base polymer can be measured as a truedensity on a pycnometer to DIN 53479 of July 1976. The density of thecured sealing composition can be determined to ISO-2781 of December 1988using a minimal quantity of a surfactant in distilled water according tothe Archimedes principle. If the cured sealing composition containshollow filling bodies, its density may lie in the range of 0.8 to 1.29g/cm³, preferably in the range of 0.85 to 1.27 g/cm³, in particular inthe range of 0.9 to 1.24 g/cm³, above all in the range of 0.95 to 1.20g/cm³.

The tensile strength was measured on dumb-bell-shaped test bodies ofcured sealing composition of the size of Type 2 with a tension speed of500 mm/min to ISO 37 of May 1994 in a Universal test machine. Thetensile strength may be at least 2.0 N/mm², preferably at least 2.05N/mm², particularly preferably at least 2.15 N/mm², above all at least2.25 N/mm² (=MPa).

The sealing composition according to the invention may also have a peelstrength of at least 90 N/25 mm, preferably of at least 125 N/25 mm. Thepeel strength represents the internal strength and in particular theadhesion of a cured sealing composition to substrates.

It was determined on specimens of cured sealing composition to AITM2-0013 with special steel wire cloth.

Surprisingly high values for peel strength and at the same time highvalues for tensile strength were achieved, even without addingepoxidated polysulfides such as e.g. ELP-3 (given in U.S. Pat. No.5,663,219). If a sealing composition according to the invention ismanufactured with an epoxidated polysulfide (=polysulfide with terminalfunctional epoxide groups, so that there is no mercapto functionality),no positive influences on tensile strength are produced to the knowledgeof the applicant.

Surprisingly however, it was found that high tensile strengths combinedwith high peel strength values can be achieved at low densities evenwithout the use of special polymers such as e.g. Permapol® P-5 orepoxidated polysulfides. However, both the epoxidated polysulfides andthe special polymers such as e.g. Permapol® P-5 are significantly moreexpensive than conventional polysulfides, as they require a laboriousadditional production step. It is therefore advantageous that unmodifiedpolysulfides are sufficient for most of the sealing compositionsaccording to the invention.

The sealing composition according to the invention may contain aproportion of lightweight polymeric strength-increasing filler such ase.g. polyamide, polyethylene, polypropylene. This filler is preferablyadded in powder form, optionally as a mixture of at least two differentfillers. The average particle size of the filler powder may be in therange of 0.5 to 80 μm, preferably in the range of 1 to 40 μm,particularly preferably in the range of 1.2 to 30 μm, most preferably inthe range of 1.5 to 20 μm. It may be advantageous to use a powder thathas been surface-modified e.g. by corona treatment or by anotheractivating treatment such as e.g. treatment of the filler surface withsilanes. Surface modification can achieve an improved bonding of thepolymeric powder into the sealing composition and thus improvedmechanical properties. Functional groups which facilitate bonding intothe base polymer, such as e.g. polysulfide, should thus be madeavailable on the surface of the powder particles. The proportion oflightweight polymeric strength-increasing filler, where this is nothollow filling bodies, may amount to 0 to 35 wt. %, the hollow fillingbody-free sealing compositions preferably having 10 to 25 wt. %,particularly preferably 14 to 22 wt. %. If at least one type each ofhollow filling bodies and lightweight polymeric strength-increasingfillers is used simultaneously, the sum of the contents is 0.3 to 35 wt.%, preferably 5 to 20 wt. %.

The density of the sealing composition according to the invention may,without a proportion of hollow filling bodies, be no more than 1.30g/cm³. A density of no more than 1.28 g/cm³ is preferably achieved,particularly preferably a density of no more than 1.26 g/cm³. Thedensity of the base composition according to the invention may, withouta proportion of hollow filling bodies, have a value of no more than1.285 g/cm³, in particular a value of up to 1.28 g/cm³, preferably avalue of up to 1.27 g/cm³, most preferably of up to 1.25 g/cm³, aboveall a value of up to 1.22 g/cm³, in particular a value of up to 1.19g/cm³.

The true density of these fillers, without taking account of hollowfilling bodies, normally lies approximately in the range of theaccompanying polymers and thus mostly in the range approximately of 0.8to 1.3 g/cm³. The polymeric filler powders may have a true density inthe range of 0.5 to 1.5 g/cm³. The inorganic filler powders may have atrue density in the range of 0.18 to 4.5 g/cm³. The latter powders may,in some cases, have a closed porosity. The density of the fillers, whichare not hollow filling bodies, may be determined to DIN 53479 of July1976 using a minimal quantity of a surfactant in de-gassed deionisedwater in a pycnometer.

The density of the hollow filling bodies may be determined in a similarway, however using a graduated measuring cylinder with a notchedplunger, which is pressed onto the surface of the volume of watercontaining the hollow filling bodies to remove the contained air, themeasuring cylinder which is closed with the notched plunger having beenshaken previously to disperse the hollow filling bodies whilst avoidingfoam formation.

The sealing composition according to the invention may have a proportionof hollow filling bodies such as e.g. polymeric hollow spheres in therange of 0.3 to 10 wt. %. The proportion of hollow filling bodies ispreferably in the range of 0.5 to 5 wt. %. Here a proportion of e.g. 2wt. % hollow filling bodies may constitute a proportion by volume of thesealing composition in the range of 15 to 35 vol. %, depending on thetype of hollow filling body. The addition of hollow filling bodies helpsto reduce the density of the sealing composition relativelysignificantly because of the extraordinarily low true density of thehollow filling bodies.

The sealing composition according to the invention may have hollowfilling bodies with an average diameter of no more than 50 μm, inparticular those of no more than 30 μm, measured under a lightmicroscope, the particles lying largely scattered on the slide.

The hollow filling bodies may have a true density in the range of 0.001to 0.8 g/cm³. The true density is preferably 0.01 to 0.6 g/cm³,particularly preferably 0.02 to 0.3 g/cm³. Hollow filling bodies may, inprinciple, consist of any material and may optionally additionally becoated. They preferably consist substantially of a ceramic material, ofglass or of an organic material such as e.g. of an aluminium-containingsilicate. In particular, they consist substantially of a polymericmaterial e.g. based on acrylonitrile copolymer or methacrylonitrilecopolymer. The shape of the hollow filling bodies is preferablysubstantially spherical. The average diameter of the hollow fillingbodies is preferably in the range of 2 to 100 μm, in particular in therange of 5 to 45 μm.

Here, lightweight filling bodies and optionally also fillers with anaverage particle size of no more than 30 μm, preferably of no more than20 μm, may be used to achieve better spreadability and mouldability ofthe sealing composition during processing.

If the average diameter of the hollow filling bodies is too large, thesealing composition will no longer be homogeneously composed andaccordingly will form inhomogeneous surfaces on curing, which restrictspossible applications, or the sealing composition will not achieve thedesired high mechanical properties. The wall thickness of the hollowfilling bodies may vary significantly, but is preferably low, to producea lower density of the sealing composition. Astonishingly, evenextremely thin-walled hollow filling bodies have scarcely ever beenpulverised in spite of severe mechanical attack during mixing of theindividual components of the sealing composition. The hollow fillingbodies are preferably filled with air, certain gases such as e.g.nitrogen or carbon dioxide, isobutane, n-pentane, isopentane and/orother waste gases from the manufacturing process.

The density of the sealing composition according to the invention thatcontains hollow filling bodies may lie in the range of 1.3 to 0.7 g/cm³,in particular in the range of less than 1.28 g/cm³, preferably less than1.25 g/cm³, particularly preferably less than 1.22 g/cm³, particularlypreferably less than 1.18 g/cm³, in particular less than 1.12 g/cm³,above all less than 1.06 g/cm³.

If a suitable base polymer, adhesion agent and polymeric filler areselected, surface modification of the polymer powder is not necessary,although it could be beneficial, because a certain level of strength isalready achieved as a result of this selection. When adding the hollowfilling bodies, the addition of structure-forming inorganic fillers forthe formation of good mechanical properties is preferred to the use ofthe polymeric filler powders. The surface properties of the polymericfiller powders have a far greater influence on the quality of thesealing compositions produced with them than the selection of thechemical type of the polymer of the polymeric filler powders.

However, in most cases, the higher the tensile strength selected forsuch sealing compositions, the lower the peel strength of these sealingcompositions. Surprisingly, it was found that this opposing correlationcan be avoided to a greater extent only if the sealing composition ismanufactured by the process according to the invention.

The composition of the sealing composition according to the invention isotherwise known in principle. The sealing composition according to theinvention may, before and after curing, additionally contain a corrosioninhibitor, in particular a chromate-free corrosion inhibitor.

For aerospace applications, it is extremely important to comply with therequirements of the specifications AIMS 04-05-001 General PurposeSpecification, AIMS 04-05-002 Fuel Tank Specification and where possiblealso the more stringent Fuel Tank Specification AIMS-04-05-012. To theknowledge of the applicant, it is extremely difficult to fulfil theminimum tensile strength requirement of 2.0 N/mm² determined to ISO 37of May 1994 in the Airbus Industries Material SpecificationAIMS-0405-012. Furthermore, achieving, the minimum peel strength of thecured sealing composition of 120 N/mm² after one thousand hours'immersion in deionised water at 35° C. in accordance with AIMS-04-05-012of November 1997 determined to AITM 2-0013 of June 1995 is problematic.It is also difficult to achieve the minimum peel strength of the curedsealing composition of 120 N/mm² after three periods of one hundredhours each of immersion in jet fuel DERD 2494 at 100° C. according toAIMS-04-05-012 determined to Airbus Industries Test Method AITM 2-0013.Most of the sealing compositions according to the invention even fulfilall of the requirements of all these specifications. This includes alsoa minimum tensile strength of 2.0 N/mm² determined to ISO 37 of May 1994in combination with a peel strength ^(Peel) of at least 120 N/25 mmdetermined to AITM 2-0013 of June 1995 and in combination with a densityof up to 1.30 g/cm³ determined to ISO 2781 of December 1988.

To the knowledge of the applicant, no single fully cured sealingcomposition has hitherto actually fulfilled all of the requirements ofthe specification AIMS 04-05-001 of November 1996 and also AIMS04-05-012 of November 1997, which are significantly higher than those ofAIMS 04-05-002 of November 1996.

The cured sealing composition according to the invention can fulfillow-temperature flexibility at −55° C. determined to ISO 1519. This isdetermined by bending a sheet coated with sealing composition over amandrel, during which process the sealing composition must remaincrack-free; the mandrel has a diameter of 10 mm.

The cured sealing composition according to the invention can have a peelstrength of at least 120 N/mm after one thousand hours' immersion indeionised water at 35° C. determined to AITM 2-0013.

The cured sealing composition according to the invention can have a peelstrength of at least 120 N/MM² after three periods of one hundred hourseach of immersion in jet fuel DERD 2494 at 100° C., determined to AITM2-0013.

The cured sealing composition according to the invention can fulfil allthe requirements of the specifications AIMS-04-05-001 andAIMS-04-05-012. It preferably fulfils all the requirements of thesespecifications, whilst also exceeding numerous limits such as density,tensile strength and peel strength as stated.

The object is also achieved by a process for the manufacture of asealing composition, which is characterised in that at least one basepolymer is mixed with at least one adhesion promoter and then the atleast one lightweight filler, in particular hollow filling bodies, isadded, a vacuum with a residual pressure of less than 50 mbar,preferably less than 10 mbar, being applied when working in thelightweight filler.

All or some of the other fillers and/or crosslinkers and furtheradditives may each be added before and/or after the at least onelightweight filler is mixed in. With the other fillers however, it ispreferable for at least part of them to be added only after mixing inthe at least one lightweight filler. It may be advantageous if thosefillers that are not readily wettable, and/or have a particularly largespecific surface area, are added before the addition of the lightweightfillers and mixed with the polymers, but that those that are readilywettable, and/or have a comparably small specific surface area, are notadded and intermixed until afterwards.

Mixing may in principle be carried out in one or more units in series.Here it is important that the base polymer and adhesion promoter arefirst mixed homogeneously with each other and lightweight filling bodiesare then admixed. The air content of the mixture thus formed must beremoved as fully as possible, to achieve good wetting and intermixing ofthe individual components. Evacuation may take place, if necessary, inanother unit. However, it is advantageous to mix intensively andevacuate at the same time. To remove as much as possible of the airadhering to the lightweight fillers and to wet the lightweight fillersas well as possible with the base polymer and the adhesion promoter.Surprisingly it was found that the mechanical stability of the hollowfilling bodies is so great that they can be mixed and worked in evenwith particularly severely and rapidly attacking mixing units, such ase.g. a dissolver, in particular a vacuum dissolver, at a high speed,without being destroyed.

With the process according to the invention for the manufacture of asealing composition, the lightweight filler can be worked in in alaboratory scale vacuum dissolver at a peripheral toothed disc speed inthe range of at least 2 m/s, in particular of at least 3 m/s,particularly preferably in the range of 5 to 15 m/s. With the processaccording to the invention for the production of a sealing compositionthe lightweight filler can be worked in in a production scale vacuumdissolver at a peripheral toothed disc speed in the range of at least 5m/s, in particular of at least 10 m/s, particularly preferably in therange of 12 to 30 m/s. Astonishingly, the hollow filling bodies were notdestroyed even with a very severe attack in the range of 18 to 22 m/s,but were so well wetted and homogeneously worked in that the mechanicalproperties of the sealing composition formed significantly improved incomparison with lower peripheral speeds and also with alternativeconventional processes for the manufacture of such sealing compositions.

In the process according to the invention, the other components of thesealing composition can then be introduced and intermixed and evacuationcan optionally take place during and/or after this process.

The non-cured or cured sealing composition according to the inventioncan be used in particular for the construction and maintenance of air-and spacecraft and for motor and rail vehicles, in shipbuilding, inapparatus engineering and mechanical engineering, in construction andcivil engineering or for the manufacture of furniture.

EXAMPLES

The subject of the invention is explained in more detail below with theaid of embodiments.

General manufacturing instructions for the lightweight sealingcompositions:

First the base polymers Thioplast® G 10 and Thiokol® LP 33 and theadhesion agents Methylon Resin 75108 and Nafturan® 8187 were provided.After the addition of lightweight fillers such as e.g. Acumist®,Dualite®, Expancel®, Rilsan® and/or Vestosint® and Aerosil® R 202 as astructure-providing filler, the components were mixed for 5 minutesunder full vacuum (<50 mbar, if possible <10 mbar) in a dissolver at aperipheral speed of ca. 3 m/sec. The chalk Winnofil® SPT or Polcarb® Swas then added as a structure-providing filler and the base compositionwas dispersed for 10 minutes at a peripheral speed of ca. 3 m/sec undervacuum (<50 mbar, if possible <10 mbar). The vacuum was applied slowlyand mixing continued until as much as possible of the waste gases hadbeen drawn off, which could be recognised also by the fact that after asignificant increase in volume, the base composition collapsed again.

If the recipe provides for the addition of deionised water, a coolingphase of 5 minutes followed, in which the material was stirred whilstcooling under full vacuum (<50 mbar, if possible <10 mbar) at aperipheral speed of ca.1 m/sec. In the final step, deionised water wasadded after cooling and homogenisation took place for 5 minutes at aperipheral speed of ca.1 m/sec and a negative pressure of 400 to 600mbar with renewed cooling. The base compositions were then left to standfor at least 1 day, before they were ready for use.

To manufacture the test bodies, the hardener Naftoseal® MC-238 B-2 wasadded to the relevant base composition at a ratio of 100:10 and the twowere mixed homogeneously, so that they formed a sealing composition.After curing, i.e. after 14 days at 23° C. and 50% relative humidity inair, the properties of the test bodies were determined. They weredetermined as stated previously in the description.

Test Series A:

This test series illustrates the influence of the manufacturing process.The base and sealing compositions according to the invention weremanufactured according to the instructions given above, whilst thereference examples were manufactured according to the conventionalmanufacturing method:

TABLE 1 Specific density and average particle sizes of the lightweightfillers used according to the manufacturers' data Specific densityAverage particle size Lightweight filler g/cm³ μm Acumist ® A-6 0.99  6Rilsan ® D 30 naturelle 1.04 20-30 Vestosint ® 2070 1-1.2  5 Vestosint ®S 7126 1-1.2 Not determined Expancel ® 551 DE 20 0.06 15-25 Expancel ®461 DE 0.06 20-40 Dualite ® 6033 0.13 25 Dualite ® 6032 0.13 70Expancel ® 091 DE 0.03 35-55

The first four lightweight fillers belong to the class of polymerpowders, the rest to the class of hollow filling bodies. The polymerpowders were used in test series B and the hollow filling bodies in testseries A and C. Aerosil® R 202, Polcarb® S and Winnofil® SPT are mineralfillers.

TABLE 2 Recipes for an improved manufacturing process in wt. % Rawmaterial Ex 1 Ex 2 Ex 3 Ex 4 1. Thioplast ® G 10 74.78 74.78 74.78 74.782. TTMA 0.21 0.21 0.21 0.21 3. Methylon Resin 75108 1.60 1.60 1.60 1.604. Nafturan ® 8187 1.64 1.64 1.64 1.64 5. Polcarb ® S 18.29 18.29 18.2918.29 6. Aerosil ® R 202 1.78 1.78 1.78 1.78 7. Expancel ® 551 DE 201.68 1.68 1.68 1.68 TTMA = Trimethylol propane trimercaptoacetate(mercapto-functional crosslinker)Manufacturing Process for Ex 1:

The base composition without lightweight filler was manufactured in theconventional way, so that first all liquid components and then allfillers except the lightweight fillers are added, mixing and evacuationbeing carried out in between and/or at the end. The low-density fillerwas then added and was intermixed at a peripheral speed of ca.1 m/s. Thematerial was then de-aerated at a residual pressure of ca.200 mbar.

Manufacturing Process for Ex 2:

The base composition without lightweight filler was manufactured in theconventional way as for Ex 1. The low-density filler was then added andintermixed at a peripheral speed of ca.1 m/s. The material was thendeaerated at a residual pressure of <50 mbar.

Manufacturing Process for Ex 3:

All components were added in weighed portions, without intermediatemixing and were then dispersed for 15 minutes at a peripheral speed ofca.3 m/s and at a vacuum of well below 50 mbar.

Manufacturing Process for Ex 4:

The composition was manufactured according to the independent processclaim of the invention, which means that the base polymer based onlong-chain linear polysulfide Thioplast® G 10 was added with theadhesion promoters Methylon Resin 75108 and Nafturan® 8187 and mixed andthe lightweight filler Expancel® 551 DE 20 (=hollow filling body) andthe filler Aerosil® R 202 were then added, a vacuum with a residualpressure well below 50 mbar and a peripheral speed of ca. 3 m/s beingapplied whilst the lightweight filler was worked in. The remainingcomponents (see table 2) were then added and mixed under a vacuum ofwell below 50 mbar and at a peripheral speed of ca. 3 m/s.

TABLE 3 Results of the measurements on the reacted sealing compositionsfor an improved manufacturing process Test Ex 1 Ex 2 Ex 3 Ex 4 Density[g/cm³] 1.06 1.08 1.10 1.09 Tensile strength [N/mm²] 1.95 2.34 2.35 2.39Elongation [%] 291 381 413 413 Peel 14 d RT [N/25 mm] 178 188 195 224

These tests showed that Ex 4, which is according to the invention notonly as a result of the properties of the cured sealing composition, butalso as a result of the manufacturing process, achieved the bestphysical properties of the cured sealing compositions in test series A.

Surprisingly, the new manufacturing process, above all the high negativepressure and intensive wetting of the lightweight fillers with the basepolymer and with the adhesion promoter, had a significant influence onthe properties of the cured sealing compositions.

Test Series B:

This test series illustrates the manufacture of base-and sealingcompositions using polymeric powders as lightweight fillers. The sealingcompositions were manufactured according to the manufacturinginstructions according to the invention in the same way as Ex 4, otherchemical components being used in some cases.

TABLE 4 Recipes using polymeric lightweight fillers with additionquantities in wt. % Raw material Ex 5 Ex 6 Ex 7 Ex 8 Ref 1 Thioplast ® G10 50.11 52.00 49.67 51.81 49.57 Thiokol ® LP 33 20.00 17.48 19.87 17.4119.84 Methylon Resin 75108 1.62 1.62 1.84 1.61 1.61 Nafturan ® 8187 1.501.50 1.49 1.49 1.49 Acumist ® A-6 8.50 17.00 — — — Rilsan ® D 30naturelle 9.80 — 19.58 — — Vestosint ® 2070 — — — 16.93 — Vestosint ® S7182 — — — — 19.84 Winnofil ® SPT 7.70 9.00 6.16 8.96 5.46 Aerosil ® R202 1.40 1.40 1.39 1.39 1.79 Water — — — 0.40 0.40 Thiokol ® LP 33 is ashort-chain, branched polysulfide base polymer. The water used wasalways deionised water.

TABLE 5 Results of measurements on the reacted sealing compositionsmanufactured according to the formulations of Table 4 Test Ex 5 Ex 6 Ex7 Ex 8 Ref 1 Density [g/cm³] 1.28 1.26 1.30 1.30 1.32 Tensile strength[N/mm²] 2.24 2.10 2.41 2.00 1.76 Elongation [%] 285 288 282 283 292 Peel14 d RT [N/25 mm] 190 263 126 262 135

It was surprising that, in spite of the comparatively small proportionsof reinforcing mineral fillers (Aerosil® R 202 and Winnofil® SPT), hightensile strengths could still be achieved.

Surprisingly it was found that in addition, the sealing compositionsfilled only with small proportions of reinforcing mineral fillers andotherwise with polymer powders also achieved good adhesion to a widevariety of substrates (metals, a wide variety of lacquers) inconjunction with high mechanical typical values.

Although the base polymer had a density of ca.1.28 g/cm³, the examplesaccording to the invention of test series B were found, as expected, tohave a sealing composition density of ≦1.30 g/cm³ even without the useof hollow filling bodies.

Test Series C:

This test series illustrates the manufacture of base or sealingcompositions using polymeric hollow filling bodies as lightweightfillers. The sealing compositions were manufactured according to themanufacturing instructions according to the invention in the same way asEx 4, other chemical components being used in some cases.

TABLE 6 Recipes using polymeric hollow filling bodies with additionquantities in wt. % Raw material Ex 9 Ex 10 Ex 11 Ex 12 Ex 13 Ref 2 Ref3 Thioplast ® G 10 50.11 55.65 55.38 54.01 74.78 54.01 55.80 Thiokol ®LP 33 20.00 19.95 19.85 19.36 — 19.36 20.00 TPTMP — — — — 0.28 — —Methylon Resin 1.62 1.62 1.61 1.57 1.60 1.57 1.62 75108 Nafturan ® 81871.00 1.30 1.49 1.45 1.64 1.45 1.50 Expancel ® 551 0.78 1.60 — — 1.68 — —DE 20 Expancel ® 461 — — 1.69 — — — — DE Dualite ® 6033 — — — 4.13 — — —Dualite ® 6032 — — — — — 4.13 — Expancel ® 091 — — — — — — 0.75 DEWinnofil ® SPT 16.20 18.42 18.33 17.88 — 17.88 18.87 Polcarb ® S — — — —18.29 — — Aerosil ® R 202 1.40 1.46 1.45 1.41 1.78 1.41 1.46 Water — —0.20 0.19 — 0.19 — TPTMP = trimethylol propane trimercaptopropionate,mercapto-functional crosslinker.

TABLE 7 Results of the measurements on the reacted sealing compositions,which were manufactured according to the formulations of table 6 Test Ex9 Ex 10 Ex 11 Ex 12 Ex 13 Ref 2 Ref 3 Density [g/cm³] 1.29 1.09 1.081.15 1.09 1.12 1.06 Tensile strength 2.64 2.55 2.26 2.21 2.07 1.58 1.80[N/mm²] Elongation [%] 389 307 280 275 472 286 426 Peel 14 d RT 209 12597 94 204 209 254 [N/25 mm]

A connection was observed between the particle size of the lightweightfillers and the mechanical properties of the sealing compositionsmanufactured with them. Thus it was found that a reduction in theaverage particle size is accompanied by an increase in the tensilestrength. The average particle size of the hollow filling bodiespreferably does not exceed 40 μm. The proportion and type of the hollowfilling bodies and the mineral fillers have a substantial influence onthe mechanical properties.

Surprisingly, cured sealing compositions could be manufactured that haveexcellent mechanical properties and nevertheless an extremely lowdensity, in some cases of less than 1.2 g/cm³.

1. A sealing composition of low density and increased tensile strengthcomprising a sulfur-containing polymer, the sealing composition having acured density of no more than 1.3 g/cm³ determined according to ISO 2781and a cured tensile strength of at least 1.9 N/mm² according to ISO 37,whereby the sealing composition has been prepared from a basecomposition containing at least two base polymers that are polysulfides,wherein the base composition comprises a) at least one sulfur-containinglong-chain liner polymer with a chain length in the range approximatelyof 1500 to 5000 g/mol and b1) at least one sulfur-containing short-chainbranched polymer with a chain length in the range approximately of 500to 2000 g/mol which has a content of trifuntional molecules or b2) atleast one polyfunctional crosslinker with a number of functional groupsn is greater than or equal to 3 or a combination of b1) and b2), whereinthe scaling composition does not include an epoxidated polysulfide.
 2. Asealing composition according to claim 1, wherein the sealingcomposition has a peel strength of at least 90 N/25 mm.
 3. A sealingcomposition according to claim 1, wherein the sealing compositionfurther comprises hollow filling bodies in the range of 0.3 to 10 wt. %.4. A sealing composition according to claim 1, further comprising alightweight polymeric strength-increasing filler.
 5. A sealingcomposition according to claim 1 having a density of not greater than1.30 g/cm³.
 6. A sealing composition according to claim 1 furthercomprising hallow filling bodies With an average diameter of not greaterthan 50 μm.
 7. A sealing composition according to claim 1, furthercomprising hollow filling bodies have a true density in the range of0.001 to 0.8 g/cm³.
 8. A sealing composition according to claim 1,further comprising a polymeric filler powder having a true density inthe range of 0.5 to 1.5 g/cm³.
 9. A sealing composition according toclaim 1, further comprising an inorganic filler powder having a truedensity in the range 0.18 to 4.5 g/cm³.
 10. A sealing compositionaccording to claim 1, further comprising a corrosion inhibitor.
 11. Asealing composition according to claim 1 having low-temperatureflexibility at −55° C. determined according to ISO
 1519. 12. A sealingcomposition according to claim 1 having a peel strength of the curedsealing composition of at least 120 N/mm² after one thousand hoursimmersion in de-ionised water at 35° C., determined according to AITM2-0013.
 13. A sealing composition according to claim 1 having a peelstrength of the cured sealing composition of at least 120 N/mm² afterthree periods of one hundred hours each of immersion in jet fuel DERD2494 at 100° C. as determined according to AITM 2-0013.
 14. A sealingcomposition according to claim 1, wherein the sealing compositionfulfills all requirements of the specifications AIMS-04-05-001 andAIMS-04-05-012.
 15. A base composition based on sulfur-containingpolymers for the manufacture of a sealing composition comprising atleast one linear polysulfide with a chain length in the rangeapproximately of 1500 to 5000 g/mol and at least one short-chainbranched polysulfide or a polythioether or a combination of these with achain length in the range approximately of 500 to 2000 g/mol, which hasa content of trifunctional molecules in particular in the range of 0.1to 5 mol. % and at least one polyfunctional crosslinker with a number offunctional groups n is greater than or equal to 3, wherein the sealingcomposition does not include an epoxidated polysulfide.
 16. A basecomposition based on sulfur-containing polymers for the manufacture of asealing composition according to claim 15, wherein, before the additionof a hardener, the base composition has a density value of no more than1.285 g/cm³.
 17. A base composition according to claim 15, comprising aproportion of hollow filling bodies in the range of 0.3 to 10 wt. %. 18.A base composition according to claim 15, comprising a lightweightpolymeric strength-increasing filler.
 19. A base composition accordingto claim 15, having a density of no more than 1.285 g/cm³.
 20. A basecomposition according to claim 15, further comprising hollow fillingbodies with an average diameter of no more than 50 μm.
 21. A basecomposition according to claim 15, comprising the hollow filling bodieshave a true density in the range of 0.001 to 0.8 g/cm³.
 22. A basecomposition according to claim 15, comprising polymeric filler powdershaving a true density in the range of 0.5 to 1.5 g/cm³.
 23. A basecomposition according to claim 15, further comprising inorganic fillerpowder having a true density in the range of 0.18 to 4.5 g/cm³.
 24. Abase composition according to claim 15, further comprising a corrosioninhibitor.
 25. A process for the manufacture of a sealing compositionaccording to claim 1 comprising: mixing at least two base polymers thatare polysulfides wherein the at least two compositions comprise a) atleast one sulfur-containing long-chain linear polymer with a chainlength in the range approximately of 1500 to 5000 g/mol and b1) at leastone sulfur-containing short-chain branched polymer with a chain lengthin the range approximately of 500 to 2000 g/mol which has a content oftrifunctional molecules or b2) at least one polyfunctional crosslinkerwith a number of functional groups n is greater than 3 or a combinationof b1) and b2) with a number of functional groups n is greater than orequal to 3, wherein the sealing composition does not include anepoxidated polysulfide; with at least one adhesion promoter, and addingat least one lightweight filler to the mixture under a vacuum with aresidual pressure of less than 50 mbar.
 26. The process for themanufacture of a sealing composition according to claim 25, wherein thelightweight filler is worked in in a vacuum dissolver at a peripheraltoothed disc speed in the range of at least 2 m/s.
 27. A process for themanufacture of a sealing composition according to claim 25, whereinadditional components of the sealing composition are introduced andintermixed.
 28. A process for the manufacture of a sealing compositionaccording to claim 25, said lightweight filler powder has an averageparticle size of no more than 30 μm.
 29. A process for the manufactureof a sealing composition according to claim 25, wherein the at least onelinear polysulfide with a chain length in the range of about 1500 to5000 g/mol, is mixed with a short-chain branched polysulfide with achain length in the range of about 500 to 2000 g/mol, which has acontent of trifunctional molecules in particular in the range of 0.1 to5 wt. % and with at least one polyfunctional crosslinker with a numberof functional groups n is greater than or equal to 3, wherein thesealing composition does not include an epoxidated polysulfide.
 30. Asealing composition according to claim 6, wherein the sealingcomposition has a peel strength at lest 125N/25 mm.
 31. A sealingcomposition according to claim 1, consisting of a sulfur-containingpolymer, the sealing composition having a cured density of no more than1.3 g/cm³ determined according to ISO 2781 and a cured tensile strengthof at least 1.9 N/mm² determined according to ISO 37 to ISO 37, wherebythe sealing composition has been prepared from a base compositionconsisting of least two base polymers that are polysulfides selected,wherein the base composition comprises a) at least one sulfur-containinglong-chain linear polymer with a chain length in the range approximatelyof 1500 to 5000 g/mol and b1) at least one sulfur-containing short-chainbranched polymer with a chain length in the range approximately of 500to 2000 g/mol which has a content of trifunctional molecules or b2) atleast one polyfunctional crosslinker with a number of functional groupsn is greater than or equal to 3 or a combination of b1) and b2).
 32. Abase composition based on sulfur-containing polymers for the manufactureof a sealing composition comprising a base polymer comprising: at leastone long-chain linear polysulfide with a chain length in the range ofabout 1500 to 5000 g/mol in combination with at least one short-chainbranched polysulfide with a chain length in the range of about 500 to2000 g/mol that comprises at least one of a trifunctional orhigher-functional molecule, and optionally at least one polyfunctionalcrosslinker having the number of functional groups n greater than orequal to 3, but not an epoxidated polysulfide, and at least one of ahollow filling body or a lightweight polymeric strength-increasingfiller.
 33. A base composition according to claim 32, wherein it has adensity value of not more than 1.285 g/cm³ before the addition of ahardener.
 34. A base composition according to claim 32, comprising from0.3 to 10 wt. % hollow filling bodies.
 35. A base composition accordingto claim 32, wherein the at least one short-chain, branched polysulfidehas a content of trifunctional molecules in the range of 0.1 to 5 mol.%.
 36. A base composition according to claim 32, wherein, without hollowfilling bodies, it has a density of not more than 1.285 g/cm³.
 37. Abase composition according to claim 32, wherein the hollow fillingbodies have an average diameter of not more than 50 μm.
 38. A basecomposition according to claim 32, wherein the hollow filling bodieshave a true density in the range of 0.001 to 0.8 g/cm³.
 39. A basecomposition according to claim 32, wherein the polymeric filler bodieshave a true density in the range of 0.5 to 1.5 g/³.
 40. A basecomposition according to claim 32, wherein the inorganic filler bodieshave a true density in the range of 0.18 to 4.5 g/cm³.
 41. A basecomposition according to claim 32, further comprising a corrosioninhibitor.
 42. A low-density, high-tensile-strength sealing compositionbased on sulfur-containing polymers, manufactured from a basecomposition according to claim 32 by mixing with hardener and having adensity after curing of not more than 1.3 g/cm³ determined according toISO 2781, a tensile strength of at least 1.9 N/mm² determined accordingto ISO 37 and a peel strength of at least 125 N/25 mm determinedaccording to AITM 2-0013 with stainless-steel wire fabric.
 43. A sealingcomposition according to claim 42, wherein it has a proportion of hollowfilling bodies such as e.g. polymeric hollow spheres in the range of 0.3to 10 wt. %.
 44. A sealing composition, according to claim 42, whereinit contains a proportion of lightweight polymeric strength-increasingfiller such as e.g. polyamide, polyethylene, polypropylene.
 45. Asealing composition according to claim 42, wherein, without a proportionof hollow filling bodies, it has a density of not more than 1.30 g/cm³.46. A sealing composition according to claim 42, wherein it has hollowfilling bodies with an average diameter of not more than 50 μm, inparticular of not more than 30 μm.
 47. A sealing composition accordingto claim 42, wherein the hollow filling bodies have a true density inthe range of 0.001 to 0.8 g/cm³.
 48. A sealing composition according toclaim 42, wherein the polymeric filler powders have a true density inthe range of 0.5 to 1.5 g/cm³.
 49. A sealing composition according toclaim 42, wherein the inorganic filler powders have a true density inthe range of 0.18 to 4.5 g/cm³.
 50. A sealing composition according toclaim 42, wherein it additionally contains a corrosion inhibitor, inparticular a chromate-free corrosion inhibitor.
 51. A sealingcomposition according to claim 42, wherein it fulfils low-temperatureflexibility at −55° C. determined to ISO
 1519. 52. A sealing compositionaccording to claim 42, wherein it has a peel strength of the curedsealing composition of at least 120 N/mm² after immersion indemineralised water for on one thousand hours at 35° C. determined toAITM 2-0013.
 53. A sealing composition according to claim 42, wherein ithas a peel strength of the cured sealing composition of at least 120N/mm² after three periods of one hundred hours each of immersion in jetfuel DERD 2494 at 100° C., determined to AITM 2-0013.
 54. A sealingcomposition according to claim 42, wherein it fulfils all requirementsof the specifications AIMS-04-05-001 and AIMS-04-05-012.
 55. A processfor the manufacture of a sealing composition according to claim 42,comprising mixing at least one base polymer according to claim 32 withat least one adhesion promoter and adding the at least one lightweightfiller under a vacuum with a residual pressure of less than 50 mbar. 56.A process for the manufacture of a sealing composition according toclaim 55 wherein the lightweight filler is incorporated in a vacuumdissolver at a peripheral speed of the toothed disc in the range of atleast 2 m/s.
 57. A process for the manufacture of a sealing compositionaccording to claim 55 wherein the other components of the sealingcomposition are then incorporated and intermixed.
 58. A process for themanufacture of a sealing composition according to claim 55, wherein thelightweight filling bodies and optionally also fillers with an averageparticle size of not more than 30 μm in order to achieve betterspreadability and mouldability of the sealing composition duringworking.
 59. A process for the manufacture of a sealing compositionaccording to claim 55 wherein the base polymer includes at least onelong-chain linear polysulfide with a chain length in the range of about1500 to 5000 g/mol is mixed with at least one short-chain branchedpolysulfide with a chain length in the range of about 500 to 2000 g/mol,which has a content of trifunctional and/or higher-functional molecules,in particular in the range of 0.1 to 5 wt. %, and optionally with atleast one polyfunctional crosslinker having the number of functionalgroups n≧3.
 60. An air or a space craft, a motor vehicle, a railvehicle, a ship, engineering equipment or furniture comprising thecomposition of claim 32.